The conventional blade tensioner utilizing a spring blade in combination with a plastic shoe was invented by E. C. Turner and John Poyser as disclosed in U.S. Pat. No. 3,490,302. The shoe is made of a material that will creep under a load and at elevated temperature, such as a rigid filled nylon. The load is provided by the blade spring continuously bearing against the plastic shoe. The shoe has a recess at one end to receive the first end of the blade spring. The shoe includes a projection at the opposite end to pass through a matching hole at the second end of the blade spring, the blade spring and the shoe being mechanically engaged together by a split pin.
U.K. Patent #986,174 (Duncan) discloses a tensioner device for driving chains consisting of a known spring secured within a synthetic strip. The strip is made of nylon or synthetic rubber which creeps when subjected to a continuous load. The width of the chain is essentially the same as the width of the strip. The tensioning device comprises a strip having a sliding fulcrum end resting on a guide and a fixed fulcrum end adjacent to the driving sprocket. The tension spring extends between and is attached to the top ends of the strip.
U.S. Pat. No. 4,921,472 (Young) discloses an improvement over the Turner/Poyser design, the chain tensioner including a blade spring and a shoe, the mechanical interlock comprising a chamber at one end of the shoe and a shoulder disposed in a passageway in the other end of the shoe. The shoe design enables the blade spring to be assembled into the shoe secured and retained therein without a pin.
These blade type tensioners are limited to a very finite range of take-up capability. The chain elongates after prolonged use, resulting in the chain tensioner losing contact with the chain. Also, although these tensioner devices are capable of providing a high initial force, the force drops off considerably with the wear of the chain. The teachings of each of the above-identified patents are herein incorporated by reference as additional background to the present invention.
What is needed is a chain tensioner apparatus that will provide greater design flexibility of desired tensioner force, increased take-up capability, more consistent tensioner force throughout the working life of the chain, and improved damping characteristics.